Emily Anthes discusses how men's bodies prepare for fatherhood.

Super Dads!

Emily Anthes talks with readers about how men's bodies prepare for fatherhood.

Science writer Emily Anthes was online at Washingtonpost.com on Thursday, June 14, to discuss the physical and hormonal changes new dads go through. An unedited transcript of the chat follows.

Emily Anthes: Hi, everyone. I'm Emily Anthes, and I just wrote a piece for Slate about the physiological changes that men go through when they become fathers. I'm here to answer (or at least try to answer) any questions you have.

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New Jersey: I found this very interesting. As a recent adoptive parent (this is my first Father's Day), I'm curious: Do these pro-parenting hormonal changes appear in dads who are not around pregnant spouses before they become parents?

Emily Anthes: That's a popular question. I'm not aware of any studies that have directly compared changes in adoptive fathers with biological fathers. There are two main theories about how these changes occur (and they're not mutually exclusive). There is some evidence that men have to spend a lot of time around pregnant mates—live with them, for instance—in order to experience some of the pre-fatherhood changes. Some also theorize that the hormonal and brain changes that occur after birth are related to contact with the baby, so those changes should appear in adoptive and non-adoptive parents alike.

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Washington: When do all these changes in the dad take place—right from the start of the pregnancy, or only when the mom is further along?

Emily Anthes: Good question. Studies show that the changes in men happen in what scientists call a U-shaped curve. That is, the so-called "symptoms" of couvade are most noticeable during the first and third trimester of a woman's pregnancy, fading away somewhat during the second trimester.

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Ligonier, Pa.: Would these hormonal changes be the same for fathers not entranced with the idea of fatherhood? Those who secretly didn't want the pregnancy? Or those not involved as much, as fathers several generations ago were not?

Emily Anthes: Interesting idea. I'm not sure how a father's mental state and attitude about parenting would play into this. Now that we're beginning to discover some of these biological phenomenon, though, it would be interesting to see if the men whose bodies are most responsive to their mates' pregnancies have any psychological, social, or other environmental factors in common.

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New York: Has there been any research to your knowledge on variability in male fathering biology? Is the line "I'd be a good father, but I'm genetically pre-disposed against it" far off?

Emily Anthes: The only research that I know of shows that there is, indeed, significant variability (even among men who are all living with pregnant women). But I don't think anyone's been able to pin down exactly what causes that variability. There could be a genetic component to it, but we don't seem to be all that close to being able to actually screen a man's genome and determine whether or not he's a "natural-born father"—if there even is such a thing.

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Alexandria, Va.: These brain changes ... might they explain the inability to do laundry to my wife's expectations? ;-P

Emily Anthes: Ha-ha. I wish I could help you out on this one, but I think that's one of the many studies of fathers that has yet to be done.

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Washington: What an interesting piece. I'm so glad you wrote about this. As a pregnant woman whose husband has gained a few pounds and—I swear—become more "maternal" these past few months, why do you think this topic isn't studied or written about more often?

Emily Anthes: I think there are a couple of reasons, which I touched on in the piece. First, I think that for a long time, the findings were simply counter-intuitive. (I wouldn't have guessed that fathers' hormones changed at all while they were waiting for a child to be born.) Second, the changes aren't that obvious—we weren't likely to accidentally discover hormone changes in male hamsters, for instance, unless we actually went looking for them. Finally, I think there's something that still a little bit politically incorrect about studying fathers instead of directing all our resources at mothers. Mothers clearly bear much of the pregnancy burden, and it makes sense to study them. (Also, women are famously neglected in medical studies, and I think some researchers felt that pregnancy and child-rearing was one domain in which women could get most of the attention).

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Washington: How long after birth do these changes persist?

Emily Anthes: One of the most interesting findings of the 2006 brain study was that fathers with older children didn't show the same brain enhancements. As offspring become more independent, the neuronal changes seem to reverse themselves.

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New York: Hi Emily—great article. I saw that one of the hormones linked to parenting is cortisol, the stress hormone. Do you know if there's any research into whether being in a high-stress environment could impact parenting, or where one would find such research?

Emily Anthes: Interesting question. It is conceivable, I suppose, that living in a stressful environment could increase cortisol and therefore spur parent-child bonding as a side effect. I'd suspect, though, that living with high levels of stress has, on balance, more negative than positive effects on parenting.

The connection between cortisol and stress has been somewhat problematic for those researching parenting, though. Obviously, as parents approach the birth of their child, stress levels will increase, and so scientists have had to be careful to separate these two effects.

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New York: Fascinating article! My question is, does this explain why Seth Rogen is so fat in "Knocked Up"?

Emily Anthes: Probably not. Remember, his character does note that Allison "is prettier" than he is on the first night they meet—before she's even pregnant.

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New York: Any sense of what the signaling mechanism is? If it's just being near a pregnant female, wouldn't males who are not the father also be affected?

Emily Anthes: I don't know what the precise signaling mechanism is or if one's been definitively proposed. It is possible (even likely) that the hormones of others who are living or spending time with a pregnant woman would also be affected. It turns out that groups of people who live together influence each others' hormones in lots of ways--girls who live with adult men, such as fathers, for instance, have been shown to start menstruating later—that we're just beginning to understand.

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New York: Do these physiological changes—both before and after the child is born—depend at all on whether the man is the biological father or has been cuckolded?

Emily Anthes: I've addressed some of the issues of biological vs. non-biological fathers above, but your mention of cuckolding is interesting. In certain mammals, it is common for males to kill infants of their own species. This behavior can be adaptive for men who aren't fathers but is obviously not adaptive if men kill their own offspring. Studies have shown though, that when a male's mate is pregnant, he becomes indiscriminately less aggressive toward all youngsters, whether or not they're his kin. This behavior keeps a male from inadvertantly attacking his own offspring, but also means that if his mate was actually impregnated by another male—either before or after he himself mated with her--he would show the same physiological changes and the same paternal behavior as if the offspring were his own.

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Washington: Great article! I hope to read more of your stuff on Slate. Was this column inspired by your own experience with pregnancy and the pseudo-pregnancy of your mate?

Emily Anthes: Good point. I'm sure that there is a tradeoff involved. But if the testosterone drop was naturally selected for, it means this tradeoff was worth it for dads. Levels of the sex hormone don't stay permanently low in men—they're just depressed when their children are the youngest. Perhaps, for the first few weeks of her life, a child is better served by having a father who's around than one who's out fighting. But that's just my own speculation. I'd imagine that a drop in testosterone doesn't preclude a father from defending the nest.

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Middleton, Wis.: Hi Emliy. Interesting topic. I became a dad 12 days ago and have been surprised at how my latent "motherly" instincts have appeared. I also have a twin sister—do you know of any studies on the effect that has on one's fatherhood? I have heard about studies showing (I believe) less testosterone among men with a twin sister. Thanks!

Emily Anthes: Congratulations on becoming a father. I don't know about that study specifically, but there are some studies in rodents (I believe) that show that males who were positioned between two females in the womb have different paternal behavior than males who were positioned between two males. I don't know all the details, but the hormonal environment of the womb does seem like it can make a difference.

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St. Paul, Minn.: I have four grandsons, and when they were born I told people—only half-joking—that I thought there were grandmother hormones because the attachment was so immediate and so much like what I experienced when my children were born. This conversation reminds me of that phenomenon. Is there any evidence that a woman's body remembers that maternal response and that it kicks in again with a new generation?

Emily Anthes: There is some anecdotal evidence that pregnant women's female relatives (sisters, mothers, mothers-in-law) can experience sympathetic pregnancy (sometimes complete with a belly to match).

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Blacksburg, Va.: My husband (ordinarily an endomorphic 6-foot, 145-pounder) gained 30 pounds during both of my pregnancies—and then lost all the weight faster than I did. Most irritating.

Emily Anthes: I bet. I'm sure there are other moms in the same boat. But take heart—maybe he was doing it all for the good of your children.

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Emily Anthes: Well, it looks like that's a wrap. Thank you for joining me. Happy Father's Day to all you dads out there.